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Three-dimensional nanoporous MoS2 framework decorated with Au nanoparticles for surface-enhanced Raman scattering
Accepted Manuscript Research paper Three-Dimensional Nanoporous MoS2 Framework Decorated with Au Nanoparticles for Surface-Enhanced Raman Scattering Yingqiang Sheng, Shouzhen Jiang, Cheng Yang, Mei Liu, Aihua Liu, Chao Zhang, Zhen Li, Yanyan Huo, Minghong Wang, Baoyuan Man PII: DOI: Reference:
S0009-2614(17)30525-0 http://dx.doi.org/10.1016/j.cplett.2017.05.069 CPLETT 34858
To appear in:
Chemical Physics Letters
Received Date: Revised Date: Accepted Date:
1 March 2017 25 May 2017 27 May 2017
Please cite this article as: Y. Sheng, S. Jiang, C. Yang, M. Liu, A. Liu, C. Zhang, Z. Li, Y. Huo, M. Wang, B. Man, Three-Dimensional Nanoporous MoS2 Framework Decorated with Au Nanoparticles for Surface-Enhanced Raman Scattering, Chemical Physics Letters (2017), doi: http://dx.doi.org/10.1016/j.cplett.2017.05.069
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Three-Dimensional Nanoporous MoS2 Framework Decorated with Au Nanoparticles for Surface-Enhanced Raman Scattering
Yingqiang Sheng a, Shouzhen Jiang a,b, Cheng Yanga,b, Mei Liua,b, Aihua Liua, Chao Zhanga,b, Zhen Lia, Yanyan Huoa, Minghong Wanga and Baoyuan Mana, a
School of Physics and Electronics, Shandong Normal University, Jinan 250014, People’s
Republic of China b
Institute of Materials and Clean Energy, Shandong Normal University, Jinan 250014,
People’s Republic of China ABSTRACT The three-dimensional (3D) MoS2 decorated with Au nanoparticles (Au NPs) hybrids (3D MoS2-Au NPs) for surface-enhanced Raman scattering (SERS) sensing was demonstrated in this paper. SEM, Raman spectroscopy, TEM, SAED, EDX and XRD were performed to characterize 3D MoS2-Au NPs hybrids. Rhodamine 6G (R6G), fluorescein and gallic acid molecules were used as the probe for the SERS detection of the 3D MoS 2-Au NPs hybrids. In addition, we modeled the enhancement of the electric field of MoS 2-Au NPs hybrids using
Corresponding author.
E-mail address:[email protected] (B.Y. Man). 1
Finite-difference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity. KEYWORDS: 3D MoS2-Au NPs hybrids, SERS activity
1. Introduction Surface-enhanced Raman scattering (SERS) as one of the most powerful detecting tools in chemical and biochemical analysis due to its high sensitivity, rapid response and finger print identification, has attracted much interests in recent decades[1]. It is believed that the two mechanisms that contribute to SERS are electromagnetic mechanism (EM) and chemical mechanism (CM)[1]. With the rapid development of the SERS technology due to its superior performance in application, a variety of novel materials as SERS substrates emerge in endlessly, such as graphene, hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS2), etc[11]. Therein, MoS2 with the high light transmission, chemical stability, biomolecular affinity and low-temperature synthesis, undoubtedly can be ideal platform to support SERS detection. Recently, many studies have been done to obtain MoS 2-noble metallic nanomaterials for SERS[11]. However, these MoS2 composite metal materials are mostly based on the twodimensional space. As three-dimensional (3D) nanostructure based SERS substrates (called 3D SERS substrates) can offer a large surface area with a high density of “hot spots”[19], building of 3D SERS substrates has been gaining much attention recently. The microstructure of 3D MoS2-Au NPs possessing large specific area and nanoporous can increase the amount of the effective hot spots and further enhance the sensitivity of the SERS signals[20]. Herein, we present a novel SERS substrate based on the MoS2-Au NPs hybrids with a 3D framework of nanometer pore sizes. The size of nanoparticles can be controlled by varying the concentration of HAuCl4·3H2O. Used R6G, fluorescein and gallic acid as the probe molecules, the prepared 3D MoS2-Au NPs hybrids has shown significant SERS ability. We 2
modeled the enhancement of the electric field of MoS 2-Au NPs hybrids using Finitedifference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity. 2. Experiment
Fig. 1. (a), (b) and (c) Schematically diagram of the synthesis process of 3D MoS2-Au NPs hybrids. (d) Schematic diagram of the 3D MoS2-Au NPs hybrids structure.
Fig. 1 shows the synthesis process of 3D MoS2-Au NPs hybrids. First, high purity of (NH4)2MoS4 (Alfa Aesar, purity of 99.99%; 0.02 g) was added to 1mL of dimethylformamide (DMF) to form a 2 wt% solution. The solution was sonicated for 20 min before use in order to prevent undissolved particles existed. The 3D network and porous structure of Ni foam was immersed into the (NH4)2MoS4 solution for about five seconds. Then substrate was placed on a hot plate at 80℃ for half an hour. Second, the Ni foam with (NH4)2MoS4 solution was placed in the quartz tube and the pressure was pumped to 5.32×10-1Pa by a mechanical pump. A gas mixture (Ar: 80 sccm and H2: 40 sccm) was introduced in the tube and the temperature
3
reached 500℃ for annealing 90 min. Third, the tube was fast cooled down to room temperature by removing the furnace. After that the sample was immersed into the PMMA solution and spun by a spin-coater at a rotating speed of 2000 rmp for 40 seconds. To investigate the SERS effect from 3D MoS2 itself without the influence of the Ni substrate, the 3D MoS2 was released by etching MoS2/nickel foam in FeCl3 solution. Finally, the etching solution was removed and replaced with deionized water. The sample was then transferred to SiO2 substrate. Then put the substrate in the furnace, flowing with a gas mixture (Ar:20 sccm and H2:40 sccm) in the furnace and the temperature reached 400℃ for annealing 60 min to remove PMMA. The prepared 3D MoS2 substrate dipped in HAuCl4·3H2O for 5 minutes.
The surface morphology of the 3D MoS2-Au NPs hybrids was characterized by scanning electron microscopy (SEM. Zeiss Gemini Ultra-55) with energy-dispersive X-ray spectroscopy (EDX) for chemical analysis. Raman spectroscopy was carried to study the SERS behaviors of substrates using a Raman spectrometer (Horiba HR Evolution 800) with laser wavelength of 532 nm, laser power of 48 mW, the diffraction grid of 1800 gr/mm and the spatial resolution of 400 nm. A 50× objective (N.A.=0.50) was used throughout the experiment. The Raman map was measured over 20×20 μm area with a step of 1 μm. The transmission electron microscopy (TEM) and selected area electron diffraction (SAED) were carried out by a transmission electron microscopy system (Hitachi H-800). The crystallinity of 3D MoS2-Au NPs hybrids was characterized by XRD (Rigaku D/MAX-RB). 4
3. Results and discussion
Fig. 2. SEM image of (a) MoS2 grown on nickel foam after thermally decomposing process. (b) 3D MoS2 networks after removal of nickel foam. SEM images of Au NPs on 3D MoS2 modified via different concentrations of HAuCl4·3H2O. (c)-(f): concentrations are 0.3 mM, 0.6 mM, 0.9 mM and 1.2 mM, respectively.
The surface morphology of the 3D MoS2-Au NPs was characterized by SEM. Fig. 2a shows the SEM image of MoS2 on Ni foam with clear porous structures. The SEM image of the MoS2-Ni foam indicate that a continuous and smooth surface of MoS 2 had successfully formed. After the Ni template removed, the MoS 2 presented a 3D network structure. (Fig. 2b) The wrinkles of 3D MoS2 are well remained without any observable crack or break. Fig. 2c-f shows the SEM images of Au NPs decorated on MoS2 framework with different HAuCl4·3H2O concentrations. The size and the grain spacing of Au NPs were changed with the variation of HAuCl4 concentration from 0.3 to 1.2 mM. For the HAuCl4 concentration of 0.3 mM, the equally distributed Au NPs exhibited a mean size of 82 nm and the average 5
distance of~40 nm (Fig. 2c). The Au NPs became relatively large and little aggregated with concentration of 0.6 mM (Fig. 2d). The mean diameter and the average distance of the Au NPs were~148 nm and~43 nm, respectively. When we increased the concentration, as shown in Fig. 2e, a uniform and high-density Au NPs were decorated on the 3D MoS2 framework. The SEM images clearly show that small NPs with a diameter around 170 nm were formed after AuCl-4 dipped. However, with further increased the HAuCl4 concentration to 1.2 mM, Au NPs became more aggregated and exhibited irregular-shaped (Fig. 2f). We propose at the beginning, the AuCl﹣ ions adsorbed onto the defective sites and the boundary in 3D MoS 2 4 layers and reduced to Au atoms which subsequently form Au nanoclusters. The defect or the boundary contained partially unbound sulfur[25], which attracted the Au3+ precursor at the initial stage and served as the first nucleation center for the Au particle growth[25]. Therefore, the sites formed gold nanoparticles seemed to be bounded with the surface of the disulfides by Au-S bonds conditioning strong fixation of the Au NPs to the 3D MoS2.
Fig. 3. (a) Raman spectra for the 3D MoS2 substrate (black line) and 3D MoS2-Au NPs substrate (red line). (b) Raman intensity of R6G (1×10-6 M) on 3D MoS2-Au NPs substrates which were modified by 6
different concentration of HAuCl4·3H2O (a: 0.3 mM, b: 0.6 mM, c: 0.9 mM, d: 1.2 mM). (c) Raman intensity of R6G at 613 cm-1 for different 3D MoS2-Au NPs substrates. (d) SERS map of the R6G peaks at 613 cm-1 on the 3D MoS2-Au NPs substrate over 20×20 μm2 areas.
To get the best SERS substrate, the R6G (1×10-6 M) was chosen to study the SERS performance of different 3D MoS2-Au NPs by using a Raman spectrometer with laser excitation at 532 nm (2.33 ev). In Fig. 3a, two Raman characteristic peaks of the E 12g and the A1g vibration are all clearly seen[22] and the stable Raman characteristic peaks indicate that the uniform 3D MoS2 had successfully synthesized. After decoration of Au NPs on the 3D MoS2 nanostructures, the Raman intensity greatly enhanced, suggesting the Au NPs had been successfully decorated on the surface of 3D MoS2. As shown in Fig. 3b, the intensity of the characteristics peak (613 cm-1) is varied on different substrates. Weak Raman signal of R6G were detected on 3D MoS2 substrates modified by the concentration of 0.3 mM HAuCl4·3H2O solution. The Raman intensity of R6G was increased after the 0.6 mM HAuCl4·3H2O treatment. When the concentration of HAuCl4·3H2O reached 0.9 mM, the intensity of Raman signal was the strongest. The excellent enhanced effect can be attribute to the uniform and dense distribution of Au NPs, which can generate more hot spots[22]. However, the Raman signal of R6G was decreased after the 1.2 mM HAuCl 4·3H2O treatment for the seriously aggregation of Au NPs. Therefore, the SERS effect of 3D MoS 2-Au NPs nanocomposite depends on the Au NPs size and density. Fig. 3c is histograms of the Raman intensity in 613 cm-1 peak for different 3D MoS2-Au NPs substrates modified by HAuCl4 with concentration of 0.3, 0.6, 0.9 and 1.2 mM. It is clearly see that Raman enhancement factor of the 3D MoS2-Au NPs SERS substrates obtained in 0.9 mM HAuCl4·3H2O is better than other substrates, which is agreement with our analysis. Thus, we can draw the conclusion that the concentration of HAuCl4·3H2O is a key factor for the 3D MoS2-Au NPs SERS substrate and the substrate modified by 0.9 mM HAuCl4 can be used as the SERS substrate to detect probe molecules in a low concentration. Fig. 3d shows the Raman mapping of vibration modes at 613 cm-1 of R6G molecules dispensed on 3D MoS 2-Au NPs substrates. The relatively smooth 7
and uniform colour distribution in the SERS map with only a little dark region indicate that the prepared 3D MoS2-Au NPs substrate possesses well homogeneity for SERS signal.
Fig. 4. (a) Low-magnification TEM image of Au NPs/3D MoS2 film (inset: high-resolution TEM images of Au NP). (b) and (c) typical HRTEM images of multilayer MoS2 and small particle (~ 5 nm) located on the 3D MoS2 films respectively. (d) The SAED pattern of the Au NPs discussed in (a).
The Au NPs/3D MoS2 was investigated by analyzing TEM and SAED. Fig. 4a is the TEM image of Au NPs/3D MoS2, where Au NPs with well-proportioned size is detected on the surface region. HRTEM image of an Au NP is shown in the inset of Fig. 4a. Abundant edge sites of MoS2 can be observe in the TEM image as shown in the Fig. 4b, which may benefit the nucleation of Au NPs. Fig. 4c displays a HRTEM image taken from the edge part of 3D MoS2. Note that Au NPs are selectively formed on the edge sites rather than on the basal plane region of 3D MoS2. Fig. 4d shows the corresponding SAED images. The SAED image 8
of typical Au NPs decorated 3D MoS2 structure exhibits three distinguished rings which can be assigned to the MoS2 (100), (110) and Au (111) planes. The sharp and strong diffraction ring of (111)Au suggests the predominant orientation and face-centred-cubic (fcc) lattice of the Au NPs. The SAED and HRTEM results suggest that the 3D MoS 2 film can served as a growth template of Au NPs along its (111) plane. The 3D MoS2 nanostructures which possess abundant edge sites are reactive toward the nucleation of Au NPs even at room temperature[24].
Fig. 5. (a) XRD patterns of 3D MoS2 and 3D MoS2-Au NPs. (b) EDX pattern of 3D MoS2-Au NPs nanocomposite deposited on SiO2 substrate (inset: overall map spectrum). STEM image (c), STEMEDX maps in S Kα1(d), Mo Lα1(e), and Au Mα1(f) signals.
We used XRD to characterize the crystal structure of the obtained 3D MoS 2 and MoS2-Au NPs substrates. The black line in Fig. 5a shows the four noteworthy peaks of MoS 2 at 2θ:14.378°, 29.026°, 44.151°, 60.144° assigned as the (002), (004), (006) and (008) respectively [Powder diffraction file (PDF) no. 37-1492]. Here, only the (002) family of diffraction peaks are observed, indicating the hexagonal structure of the MoS2 without any 9
other impurities and a high crystallinity. For the Au NPs/3D MoS2 (red line), except the four noteworthy peaks (002), (004), (006) and (008), diffraction peaks at 38.184°, 44.392°, 64.576° and 77.547° are also found, which are assigned to (111), (200), (220) and (311) of Au[25], indicating that the face-centered cubic (fcc) Au NPs has been successfully deposited on 3D MoS2 surface. The differences in XRD patterns between 3D MoS 2 and 3D MoS2-Au NPs may be ascribed to the reaction, the MoS 2 components change before and after reaction with HAuCl4. EDX image of 3D MoS2-Au NPs nanocomposite (Fig. 5b) shows the peaks corresponding to C, O, Si, S, Mo, Au and Ni elements. The inset is the overall map spectrum of 3D MoS2-Au NPs. Presence of Ni signal is due to the residual part of the nickel foam. The local composition of the gold-decorated 3D MoS2 is also studied with high resolution using STEM-EDX point spectra (Fig. 5c-f), which have clearly shown the presence of gold in the grown nanoparticles.
Fig. 6. (a) Raman spectra of R6G on the 3D MoS2-Au NPs substrate from 10-4-10-9 M at 532 nm laser excitation. (b) Raman intensity of R6G peaks at 613cm-1 as a function of concentration in log scale. (c) Raman signals of R6G on SiO2 substrate with concentration 10-3 M. (d) Raman spectrum of R6G (1×10-6 M) on the 3D MoS2 substrate and 3D MoS2-Au NPs substrate. (e)-(f) Raman spectra of 10-5 M 10
fluorescein and gallic acid on the 3D MoS2-Au NPs substrate (red curve) and SiO2 substrate (black curve).
To test the SERS ability of the 3D MoS2-Au NPs substrate, R6G, fluorescein and gallic acid were used. Fig. 6a exhibits the SERS spectra of R6G with different concentrations adsorbed on the substrate. The Raman peaks at 613, 774, 1186, 1362, 1507, and 1651 cm-1 are observed in the region from 500 to 1800 cm-1 as shown in Fig. 6a. According to the SERS selection rules[25], we think the strong intensity of the vibration mode (613 cm-1) in the SERS of R6G assigned to the C-C-C bond is perpendicular to the surfaces of Au NPs. From Fig. 6b, the coefficient of determination (R2) of the linear fit calibration curve for the peaks of 613 cm-1 is reached 0.95. These results indicate 3D MoS 2-Au NPs substrate could provide reliable and clear SERS signals. As comparison, the R6G (1×10-3 M, 1×10-6 M) was also drop-casted onto the bare SiO2 substrate and 3D MoS2 for Raman signal detection. At the resonant wavelength excitation (532 nm) of R6G, the phonon peaks are hidden by the strong fluorescent background and only small vibration mode is observed on the R6G/SiO 2 substrate (Fig. 6c). When collected Raman spectrum from the R6G/3D MoS 2 substrate, partial peaks with lower intensity could be detected (Fig. 6d, the black line). In contrast to this, the distinct peaks with high intensity are observed on the R6G/3D MoS 2-Au NPs substrate (Fig. 6d, the red line). This is probably due to fluorescence quenching by gold nanoparticles. Since MoS2 interact with Au NPs tightly, the narrow gap between MoS2 and Au NPs will play important role in producing SERS effect[25]. To assess the detection sensitivity of 3D MoS 2-Au NPs hybrid system, fluorescein and gallic acid molecules were also selected for investigating the feasibility of molecular detection based on the substrates. As shown in Fig. 6e-f, compared with the SERS spectra on the SiO2 substrate, those recorded on the 3D MoS2-Au NPs substrates show clearly SERS features and improved signal-to-noise ratio, which indicates that the use of 3D MoS2-Au NPs hybrid system for molecular detection in feasible. The SERS enhancement factors (EF) for R6G on the 3D MoS 2-Au NPs substrate was calculated according to the standard equation [33]. 11
EF＝
I SERS / N SERS , I RS / N RS
where ISERS and IRS, represent the peak intensities of the SERS spectra and the normal Raman spectra respectively, NSERS and NRS are, respectively, the numbers of R6G molecules on the substrates within the laser spot. The average EF is calculated to be 1.1×103 for the 3D MoS2Au NPs substrates. Similarly, the EF for the 3D MoS 2 substrates is calculated to be 3.6×102. As a comparison, the SERS signals of 3D MoS 2-Au NPs are ~ 3.1 times stronger than that of 3D MoS2.
Fig. 7. (a) is the top view of the electric field distribution on the MoS2 sample. (b)-(d) are the side views of the electric field distribution on the diameter of 82 nm, 148 nm and 170 nm Au/3D MoS2 with the gap of 40 nm, respectively.
We calculated and analyzed the local electric field properties using commercial COMSOL software. We built the theoretical model as the structure shown in Fig. 1d, between the top 12
and bottom of Au NPs is 5 layers of MoS 2. In fact, we also attempted to model the enhancement of the electric field of 3D MoS2 modified by 1.2 mM HAuCl4. However, the irregular shape made it hard to model the Au NPs in an ideal model. To study the size effect on the enhanced electromagnetic field, we set the diameter of Au NPs respectively to 82, 148 and 170 nm, which is corresponding with the experimental parameters. Just as exhibit in Fig. 7b-d, the hot spots of MoS2-Au NPs structure significantly between the Au NPs and 3D MoS 2. The magnitude of electrical field with 170 nm Au NPs is approximately 2.4 times larger than that with 82 nm Au NPs. Compared three different sizes of Au NPs SERS substrates, the density for the local electric field is increased with increase size of the gold particles. Just as our expect, the density for the local electric field on the 3D MoS2 Au NPs is ~ 3.4 times stronger than that of 3D MoS 2, which is well consistent with the experimental results (3.1 times stronger). 4. Conclusions In conclusion, we have been synthesized 3D-foam-like MoS2-Au NPs nanostructure by a thermally decomposing method with nickel foam as substrates. The size and number density of the Au NPs can be further controlled by tuning the concetration of HAuCl4·3H2O. Benefit from their high specific surface area hierarchical porous structures, high dispersion and affinity of Au NPs in interconnected macroporous framework, the fabricated SERS substrates exhibit high sensitively. These SERS behaviors are also confirmed by theory calculation via a commercial COMSOL software. This new kind of 3D MoS2-Au NPs sample is expected to broaden the study in nano-electronic devices, especially in microanalysis. Acknowledgments The authors are grateful for financial support from the National Science Foundation of China (11474187, 11274204, 11674199 and 11504209), Excellent Young Scholars Research Fund of Shandong Normal University.
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References [1] M. Moskovits, J. Raman. Spectrosc. 36 (2005) 485-496. [2] K. Kneipp, H. Kneipp, J. Kneipp, Accounts. Chem. Res. 39 (2006) 443-450. [3] Alvarez-Puebla, A. Ramón, L.M. Liz-Marzán, Small. 6 (2010) 604-610. [4] M.P. Cecchini, V.A. Turek, J. Paget, A.A. Kornyshev, J.B. Edel, Nat. Mater. 12 (2013) 165-171. [5] A. Campion, P. Kambhampati, Chem. Soc. Rev. 27 (1998) 241-250. [6] D. Cialla, A. März, R. Böhme, F. Theil, K. Weber, M. Schmitt, J. Popp, Anal. Bioanal. Chem. 403 (2012) 27–54. [7] J.P. Singh, H.Y. Chu, J. Abell, R.A. Tripp, Y. Zhao, Nanoscale. 4 (2012) 3410–3414. [8] E.C. Le Ru, E. Blackie, M. Meyer, P.G. Etchegoin, J. Phys. Chem. C. 111 (2007) 1379413803. [9] S. Huang, X. Ling, L. Liang, Y. Song, W. Fang, J. Zhang, M.S. Dresselhaus, Nano. Lett. 15 (2015) 2892-2901. [10] M. Moskovits, PHYS. CHEM. CHEM. PHYS. 15 (2013) 5301-5311. [11] H. Qiu, Z. Li, S. Gao, P. Chen, C. Zhang, S. Jiang, H. Li, RSC. ADV. 5 (2015) 8389983905. [12] Z. Dai, X. Xiao, W. Wu, Y. Zhang, L. Liao, S. Guo, C. Jiang, LIGHT-SCI. APPL. 4 (2015) e342. [13] S. Su, C. Zhang, L. Yuwen, J. Chao, X. Zuo, X. Liu, L. Wang, Acs. Appl. Mater. Inter. 6 (2014) 18735-18741.
14
[14] H. Zhou, F. Yu, C.F. Guo, Z. Wang, Y. Lan, G. Wang, Z. Ren, Nanoscale. 7 (2015) 9153-9157. [15] J. Lu, J.H. Lu, H. Liu, B. Liu, L. Gong, E.S. Tok, C.H. Sow, Small. 11 (2015)1792-1800. [16] Y. Shi, J.K. Huang, L. Jin, Y.T. Hsu, S.F. Yu, L.J. Li, H.Y. Yang, Sci. Rep. 3 (2013) 1839. [17] Q. Ding, Y. Shi, M. Chen, H. Li, X. Yang, Y. Qu, M. Sun, Sci. Rep. 6 (2016). [18] X. Yang, H. Yu, X. Guo, Q. Ding, T. Pullerits, R. Wang, M. Sun, Materials Today Energy. 5 (2017) 72-78. [19] Y. Qian, G. Meng, Q. Huang, C. Zhu, Z. Huang, K. Sun, B. Chen, Nanoscale. 6 (2014) 4781-4788. [20] C. Zhang, B.Y. Man, S.Z. Jiang, C. Yang, M. Liu, C.S. Chen, Z. Li, Appl. Surf. Sci. 347 (2015) 668-672. [21] T.S. Sreeprasad, P. Nguyen, N. Kim, V. Berry, Nano.Lett. 13 (2013) 4434-4441. [22] C. Lee, H. Yan, L.E. Brus, T.F. Heinz, J. Hone, S. Ryu, Acs. Nano. 4 (2010) 2695-2700. [23] J. Chen, T. Mårtensson, K.A. Dick, K. Deppert, H. Xu, L. Samuelson, H. Xu, Nanotechnology. 19 (2008) 275712. [24] A.Y. Polyakov, L. Yadgarov, R. Popovitz-Biro, V.A. Lebedev, I. Pinkas, R. Rosentsveig, R. Tenne, J. Phys. Chem. C. 118 (2014) 2161-2169. [25] F. Ochanda, W.E. Jones, Langmuir. 21 (2005) 10791-10796. [26] M. Moskovits, J. Chem. Phys. 77 (1982) 4408-4416. [27] M. Moskovits, J. Phys. Chem. 92 (1988) 6327-6329. [28] G. Lu, H. Li, C. Liusman, Z. Yin, S. Wu, H. Zhang, Chem. Sci. 2 (2011) 1817-1821. 15
[29] X. Ling, L. Xie, Y. Fang, H. Xu, H. Zhang, J. Kong, Z. Liu, Nano. Lett. 10 (2009) 553561. [30] A.M. Michaels, M. Nirmal, L.E. Brus, J. Am. Chem. Soc. 121 (1999) 9932-9939. [31] S. Nie, S.R. Emory, Science. 275 (1997) 1102-1106. [32] C. Zhang, S.Z. Jiang, C. Yang, C.H. Li, Y.Y. Huo, X.Y. Liu, B.Y. Man, Sci. Rep. 6 (2016). [33] E.C. Le Ru, E. Blackie, M. Meyer, P.G. Etchegoin, J. Phys. Chem. C. 111 (2007) 1379413803. [34] Z. Huang, G. Meng, Q. Huang, B. Chen, C. Zhu, Z. Zhang, J. Raman. Spectrosc. 44 (2013) 240-246. [35] C.C Kuo, C.H. Chen, Nanoscale. 6 (2014) 12805-12813.
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Highlights 1. We present a novel SERS substrate based on the MoS 2-Au NPs hybrids with a 3D framework. 2. 3D MoS2-Au NPs possess large specific area and the nanoporous structure increase the amount of the hot spots. 3. The size of gold nanoparticles is controlled by varying the concentration of HAuCl4·3H2O. 4. The morphologies and performance of 3D MoS 2-Au NPs were characterized by SEM, Raman spectroscopy, TEM, SAED, EDX and XRD. 5. We modeled the enhancement of the electric field of 3D MoS 2-Au NPs hybrids using FDTD analysis.
Graphical abstract
The three-dimensional MoS2 decorated with Au nanoparticles hybrids for surface-enhanced Raman scattering (SERS) sensing was demonstrated in this paper. The size of nanoparticles can be controlled by varying the concentration of HAuCl4·3H2O. Used R6G as the probe molecule, the prepared 3D MoS2-Au NPs hybrids has shown significant SERS ability. We modeled the enhancement of the electric field of MoS2-Au NPs hybrids using Finite-difference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity.
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S0009-2614(17)30525-0 http://dx.doi.org/10.1016/j.cplett.2017.05.069 CPLETT 34858
To appear in:
Chemical Physics Letters
Received Date: Revised Date: Accepted Date:
1 March 2017 25 May 2017 27 May 2017
Please cite this article as: Y. Sheng, S. Jiang, C. Yang, M. Liu, A. Liu, C. Zhang, Z. Li, Y. Huo, M. Wang, B. Man, Three-Dimensional Nanoporous MoS2 Framework Decorated with Au Nanoparticles for Surface-Enhanced Raman Scattering, Chemical Physics Letters (2017), doi: http://dx.doi.org/10.1016/j.cplett.2017.05.069
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Three-Dimensional Nanoporous MoS2 Framework Decorated with Au Nanoparticles for Surface-Enhanced Raman Scattering
Yingqiang Sheng a, Shouzhen Jiang a,b, Cheng Yanga,b, Mei Liua,b, Aihua Liua, Chao Zhanga,b, Zhen Lia, Yanyan Huoa, Minghong Wanga and Baoyuan Mana, a
School of Physics and Electronics, Shandong Normal University, Jinan 250014, People’s
Republic of China b
Institute of Materials and Clean Energy, Shandong Normal University, Jinan 250014,
People’s Republic of China ABSTRACT The three-dimensional (3D) MoS2 decorated with Au nanoparticles (Au NPs) hybrids (3D MoS2-Au NPs) for surface-enhanced Raman scattering (SERS) sensing was demonstrated in this paper. SEM, Raman spectroscopy, TEM, SAED, EDX and XRD were performed to characterize 3D MoS2-Au NPs hybrids. Rhodamine 6G (R6G), fluorescein and gallic acid molecules were used as the probe for the SERS detection of the 3D MoS 2-Au NPs hybrids. In addition, we modeled the enhancement of the electric field of MoS 2-Au NPs hybrids using
Corresponding author.
E-mail address:[email protected] (B.Y. Man). 1
Finite-difference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity. KEYWORDS: 3D MoS2-Au NPs hybrids, SERS activity
1. Introduction Surface-enhanced Raman scattering (SERS) as one of the most powerful detecting tools in chemical and biochemical analysis due to its high sensitivity, rapid response and finger print identification, has attracted much interests in recent decades[1]. It is believed that the two mechanisms that contribute to SERS are electromagnetic mechanism (EM) and chemical mechanism (CM)[1]. With the rapid development of the SERS technology due to its superior performance in application, a variety of novel materials as SERS substrates emerge in endlessly, such as graphene, hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS2), etc[11]. Therein, MoS2 with the high light transmission, chemical stability, biomolecular affinity and low-temperature synthesis, undoubtedly can be ideal platform to support SERS detection. Recently, many studies have been done to obtain MoS 2-noble metallic nanomaterials for SERS[11]. However, these MoS2 composite metal materials are mostly based on the twodimensional space. As three-dimensional (3D) nanostructure based SERS substrates (called 3D SERS substrates) can offer a large surface area with a high density of “hot spots”[19], building of 3D SERS substrates has been gaining much attention recently. The microstructure of 3D MoS2-Au NPs possessing large specific area and nanoporous can increase the amount of the effective hot spots and further enhance the sensitivity of the SERS signals[20]. Herein, we present a novel SERS substrate based on the MoS2-Au NPs hybrids with a 3D framework of nanometer pore sizes. The size of nanoparticles can be controlled by varying the concentration of HAuCl4·3H2O. Used R6G, fluorescein and gallic acid as the probe molecules, the prepared 3D MoS2-Au NPs hybrids has shown significant SERS ability. We 2
modeled the enhancement of the electric field of MoS 2-Au NPs hybrids using Finitedifference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity. 2. Experiment
Fig. 1. (a), (b) and (c) Schematically diagram of the synthesis process of 3D MoS2-Au NPs hybrids. (d) Schematic diagram of the 3D MoS2-Au NPs hybrids structure.
Fig. 1 shows the synthesis process of 3D MoS2-Au NPs hybrids. First, high purity of (NH4)2MoS4 (Alfa Aesar, purity of 99.99%; 0.02 g) was added to 1mL of dimethylformamide (DMF) to form a 2 wt% solution. The solution was sonicated for 20 min before use in order to prevent undissolved particles existed. The 3D network and porous structure of Ni foam was immersed into the (NH4)2MoS4 solution for about five seconds. Then substrate was placed on a hot plate at 80℃ for half an hour. Second, the Ni foam with (NH4)2MoS4 solution was placed in the quartz tube and the pressure was pumped to 5.32×10-1Pa by a mechanical pump. A gas mixture (Ar: 80 sccm and H2: 40 sccm) was introduced in the tube and the temperature
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reached 500℃ for annealing 90 min. Third, the tube was fast cooled down to room temperature by removing the furnace. After that the sample was immersed into the PMMA solution and spun by a spin-coater at a rotating speed of 2000 rmp for 40 seconds. To investigate the SERS effect from 3D MoS2 itself without the influence of the Ni substrate, the 3D MoS2 was released by etching MoS2/nickel foam in FeCl3 solution. Finally, the etching solution was removed and replaced with deionized water. The sample was then transferred to SiO2 substrate. Then put the substrate in the furnace, flowing with a gas mixture (Ar:20 sccm and H2:40 sccm) in the furnace and the temperature reached 400℃ for annealing 60 min to remove PMMA. The prepared 3D MoS2 substrate dipped in HAuCl4·3H2O for 5 minutes.
The surface morphology of the 3D MoS2-Au NPs hybrids was characterized by scanning electron microscopy (SEM. Zeiss Gemini Ultra-55) with energy-dispersive X-ray spectroscopy (EDX) for chemical analysis. Raman spectroscopy was carried to study the SERS behaviors of substrates using a Raman spectrometer (Horiba HR Evolution 800) with laser wavelength of 532 nm, laser power of 48 mW, the diffraction grid of 1800 gr/mm and the spatial resolution of 400 nm. A 50× objective (N.A.=0.50) was used throughout the experiment. The Raman map was measured over 20×20 μm area with a step of 1 μm. The transmission electron microscopy (TEM) and selected area electron diffraction (SAED) were carried out by a transmission electron microscopy system (Hitachi H-800). The crystallinity of 3D MoS2-Au NPs hybrids was characterized by XRD (Rigaku D/MAX-RB). 4
3. Results and discussion
Fig. 2. SEM image of (a) MoS2 grown on nickel foam after thermally decomposing process. (b) 3D MoS2 networks after removal of nickel foam. SEM images of Au NPs on 3D MoS2 modified via different concentrations of HAuCl4·3H2O. (c)-(f): concentrations are 0.3 mM, 0.6 mM, 0.9 mM and 1.2 mM, respectively.
The surface morphology of the 3D MoS2-Au NPs was characterized by SEM. Fig. 2a shows the SEM image of MoS2 on Ni foam with clear porous structures. The SEM image of the MoS2-Ni foam indicate that a continuous and smooth surface of MoS 2 had successfully formed. After the Ni template removed, the MoS 2 presented a 3D network structure. (Fig. 2b) The wrinkles of 3D MoS2 are well remained without any observable crack or break. Fig. 2c-f shows the SEM images of Au NPs decorated on MoS2 framework with different HAuCl4·3H2O concentrations. The size and the grain spacing of Au NPs were changed with the variation of HAuCl4 concentration from 0.3 to 1.2 mM. For the HAuCl4 concentration of 0.3 mM, the equally distributed Au NPs exhibited a mean size of 82 nm and the average 5
distance of~40 nm (Fig. 2c). The Au NPs became relatively large and little aggregated with concentration of 0.6 mM (Fig. 2d). The mean diameter and the average distance of the Au NPs were~148 nm and~43 nm, respectively. When we increased the concentration, as shown in Fig. 2e, a uniform and high-density Au NPs were decorated on the 3D MoS2 framework. The SEM images clearly show that small NPs with a diameter around 170 nm were formed after AuCl-4 dipped. However, with further increased the HAuCl4 concentration to 1.2 mM, Au NPs became more aggregated and exhibited irregular-shaped (Fig. 2f). We propose at the beginning, the AuCl﹣ ions adsorbed onto the defective sites and the boundary in 3D MoS 2 4 layers and reduced to Au atoms which subsequently form Au nanoclusters. The defect or the boundary contained partially unbound sulfur[25], which attracted the Au3+ precursor at the initial stage and served as the first nucleation center for the Au particle growth[25]. Therefore, the sites formed gold nanoparticles seemed to be bounded with the surface of the disulfides by Au-S bonds conditioning strong fixation of the Au NPs to the 3D MoS2.
Fig. 3. (a) Raman spectra for the 3D MoS2 substrate (black line) and 3D MoS2-Au NPs substrate (red line). (b) Raman intensity of R6G (1×10-6 M) on 3D MoS2-Au NPs substrates which were modified by 6
different concentration of HAuCl4·3H2O (a: 0.3 mM, b: 0.6 mM, c: 0.9 mM, d: 1.2 mM). (c) Raman intensity of R6G at 613 cm-1 for different 3D MoS2-Au NPs substrates. (d) SERS map of the R6G peaks at 613 cm-1 on the 3D MoS2-Au NPs substrate over 20×20 μm2 areas.
To get the best SERS substrate, the R6G (1×10-6 M) was chosen to study the SERS performance of different 3D MoS2-Au NPs by using a Raman spectrometer with laser excitation at 532 nm (2.33 ev). In Fig. 3a, two Raman characteristic peaks of the E 12g and the A1g vibration are all clearly seen[22] and the stable Raman characteristic peaks indicate that the uniform 3D MoS2 had successfully synthesized. After decoration of Au NPs on the 3D MoS2 nanostructures, the Raman intensity greatly enhanced, suggesting the Au NPs had been successfully decorated on the surface of 3D MoS2. As shown in Fig. 3b, the intensity of the characteristics peak (613 cm-1) is varied on different substrates. Weak Raman signal of R6G were detected on 3D MoS2 substrates modified by the concentration of 0.3 mM HAuCl4·3H2O solution. The Raman intensity of R6G was increased after the 0.6 mM HAuCl4·3H2O treatment. When the concentration of HAuCl4·3H2O reached 0.9 mM, the intensity of Raman signal was the strongest. The excellent enhanced effect can be attribute to the uniform and dense distribution of Au NPs, which can generate more hot spots[22]. However, the Raman signal of R6G was decreased after the 1.2 mM HAuCl 4·3H2O treatment for the seriously aggregation of Au NPs. Therefore, the SERS effect of 3D MoS 2-Au NPs nanocomposite depends on the Au NPs size and density. Fig. 3c is histograms of the Raman intensity in 613 cm-1 peak for different 3D MoS2-Au NPs substrates modified by HAuCl4 with concentration of 0.3, 0.6, 0.9 and 1.2 mM. It is clearly see that Raman enhancement factor of the 3D MoS2-Au NPs SERS substrates obtained in 0.9 mM HAuCl4·3H2O is better than other substrates, which is agreement with our analysis. Thus, we can draw the conclusion that the concentration of HAuCl4·3H2O is a key factor for the 3D MoS2-Au NPs SERS substrate and the substrate modified by 0.9 mM HAuCl4 can be used as the SERS substrate to detect probe molecules in a low concentration. Fig. 3d shows the Raman mapping of vibration modes at 613 cm-1 of R6G molecules dispensed on 3D MoS 2-Au NPs substrates. The relatively smooth 7
and uniform colour distribution in the SERS map with only a little dark region indicate that the prepared 3D MoS2-Au NPs substrate possesses well homogeneity for SERS signal.
Fig. 4. (a) Low-magnification TEM image of Au NPs/3D MoS2 film (inset: high-resolution TEM images of Au NP). (b) and (c) typical HRTEM images of multilayer MoS2 and small particle (~ 5 nm) located on the 3D MoS2 films respectively. (d) The SAED pattern of the Au NPs discussed in (a).
The Au NPs/3D MoS2 was investigated by analyzing TEM and SAED. Fig. 4a is the TEM image of Au NPs/3D MoS2, where Au NPs with well-proportioned size is detected on the surface region. HRTEM image of an Au NP is shown in the inset of Fig. 4a. Abundant edge sites of MoS2 can be observe in the TEM image as shown in the Fig. 4b, which may benefit the nucleation of Au NPs. Fig. 4c displays a HRTEM image taken from the edge part of 3D MoS2. Note that Au NPs are selectively formed on the edge sites rather than on the basal plane region of 3D MoS2. Fig. 4d shows the corresponding SAED images. The SAED image 8
of typical Au NPs decorated 3D MoS2 structure exhibits three distinguished rings which can be assigned to the MoS2 (100), (110) and Au (111) planes. The sharp and strong diffraction ring of (111)Au suggests the predominant orientation and face-centred-cubic (fcc) lattice of the Au NPs. The SAED and HRTEM results suggest that the 3D MoS 2 film can served as a growth template of Au NPs along its (111) plane. The 3D MoS2 nanostructures which possess abundant edge sites are reactive toward the nucleation of Au NPs even at room temperature[24].
Fig. 5. (a) XRD patterns of 3D MoS2 and 3D MoS2-Au NPs. (b) EDX pattern of 3D MoS2-Au NPs nanocomposite deposited on SiO2 substrate (inset: overall map spectrum). STEM image (c), STEMEDX maps in S Kα1(d), Mo Lα1(e), and Au Mα1(f) signals.
We used XRD to characterize the crystal structure of the obtained 3D MoS 2 and MoS2-Au NPs substrates. The black line in Fig. 5a shows the four noteworthy peaks of MoS 2 at 2θ:14.378°, 29.026°, 44.151°, 60.144° assigned as the (002), (004), (006) and (008) respectively [Powder diffraction file (PDF) no. 37-1492]. Here, only the (002) family of diffraction peaks are observed, indicating the hexagonal structure of the MoS2 without any 9
other impurities and a high crystallinity. For the Au NPs/3D MoS2 (red line), except the four noteworthy peaks (002), (004), (006) and (008), diffraction peaks at 38.184°, 44.392°, 64.576° and 77.547° are also found, which are assigned to (111), (200), (220) and (311) of Au[25], indicating that the face-centered cubic (fcc) Au NPs has been successfully deposited on 3D MoS2 surface. The differences in XRD patterns between 3D MoS 2 and 3D MoS2-Au NPs may be ascribed to the reaction, the MoS 2 components change before and after reaction with HAuCl4. EDX image of 3D MoS2-Au NPs nanocomposite (Fig. 5b) shows the peaks corresponding to C, O, Si, S, Mo, Au and Ni elements. The inset is the overall map spectrum of 3D MoS2-Au NPs. Presence of Ni signal is due to the residual part of the nickel foam. The local composition of the gold-decorated 3D MoS2 is also studied with high resolution using STEM-EDX point spectra (Fig. 5c-f), which have clearly shown the presence of gold in the grown nanoparticles.
Fig. 6. (a) Raman spectra of R6G on the 3D MoS2-Au NPs substrate from 10-4-10-9 M at 532 nm laser excitation. (b) Raman intensity of R6G peaks at 613cm-1 as a function of concentration in log scale. (c) Raman signals of R6G on SiO2 substrate with concentration 10-3 M. (d) Raman spectrum of R6G (1×10-6 M) on the 3D MoS2 substrate and 3D MoS2-Au NPs substrate. (e)-(f) Raman spectra of 10-5 M 10
fluorescein and gallic acid on the 3D MoS2-Au NPs substrate (red curve) and SiO2 substrate (black curve).
To test the SERS ability of the 3D MoS2-Au NPs substrate, R6G, fluorescein and gallic acid were used. Fig. 6a exhibits the SERS spectra of R6G with different concentrations adsorbed on the substrate. The Raman peaks at 613, 774, 1186, 1362, 1507, and 1651 cm-1 are observed in the region from 500 to 1800 cm-1 as shown in Fig. 6a. According to the SERS selection rules[25], we think the strong intensity of the vibration mode (613 cm-1) in the SERS of R6G assigned to the C-C-C bond is perpendicular to the surfaces of Au NPs. From Fig. 6b, the coefficient of determination (R2) of the linear fit calibration curve for the peaks of 613 cm-1 is reached 0.95. These results indicate 3D MoS 2-Au NPs substrate could provide reliable and clear SERS signals. As comparison, the R6G (1×10-3 M, 1×10-6 M) was also drop-casted onto the bare SiO2 substrate and 3D MoS2 for Raman signal detection. At the resonant wavelength excitation (532 nm) of R6G, the phonon peaks are hidden by the strong fluorescent background and only small vibration mode is observed on the R6G/SiO 2 substrate (Fig. 6c). When collected Raman spectrum from the R6G/3D MoS 2 substrate, partial peaks with lower intensity could be detected (Fig. 6d, the black line). In contrast to this, the distinct peaks with high intensity are observed on the R6G/3D MoS 2-Au NPs substrate (Fig. 6d, the red line). This is probably due to fluorescence quenching by gold nanoparticles. Since MoS2 interact with Au NPs tightly, the narrow gap between MoS2 and Au NPs will play important role in producing SERS effect[25]. To assess the detection sensitivity of 3D MoS 2-Au NPs hybrid system, fluorescein and gallic acid molecules were also selected for investigating the feasibility of molecular detection based on the substrates. As shown in Fig. 6e-f, compared with the SERS spectra on the SiO2 substrate, those recorded on the 3D MoS2-Au NPs substrates show clearly SERS features and improved signal-to-noise ratio, which indicates that the use of 3D MoS2-Au NPs hybrid system for molecular detection in feasible. The SERS enhancement factors (EF) for R6G on the 3D MoS 2-Au NPs substrate was calculated according to the standard equation [33]. 11
EF＝
I SERS / N SERS , I RS / N RS
where ISERS and IRS, represent the peak intensities of the SERS spectra and the normal Raman spectra respectively, NSERS and NRS are, respectively, the numbers of R6G molecules on the substrates within the laser spot. The average EF is calculated to be 1.1×103 for the 3D MoS2Au NPs substrates. Similarly, the EF for the 3D MoS 2 substrates is calculated to be 3.6×102. As a comparison, the SERS signals of 3D MoS 2-Au NPs are ~ 3.1 times stronger than that of 3D MoS2.
Fig. 7. (a) is the top view of the electric field distribution on the MoS2 sample. (b)-(d) are the side views of the electric field distribution on the diameter of 82 nm, 148 nm and 170 nm Au/3D MoS2 with the gap of 40 nm, respectively.
We calculated and analyzed the local electric field properties using commercial COMSOL software. We built the theoretical model as the structure shown in Fig. 1d, between the top 12
and bottom of Au NPs is 5 layers of MoS 2. In fact, we also attempted to model the enhancement of the electric field of 3D MoS2 modified by 1.2 mM HAuCl4. However, the irregular shape made it hard to model the Au NPs in an ideal model. To study the size effect on the enhanced electromagnetic field, we set the diameter of Au NPs respectively to 82, 148 and 170 nm, which is corresponding with the experimental parameters. Just as exhibit in Fig. 7b-d, the hot spots of MoS2-Au NPs structure significantly between the Au NPs and 3D MoS 2. The magnitude of electrical field with 170 nm Au NPs is approximately 2.4 times larger than that with 82 nm Au NPs. Compared three different sizes of Au NPs SERS substrates, the density for the local electric field is increased with increase size of the gold particles. Just as our expect, the density for the local electric field on the 3D MoS2 Au NPs is ~ 3.4 times stronger than that of 3D MoS 2, which is well consistent with the experimental results (3.1 times stronger). 4. Conclusions In conclusion, we have been synthesized 3D-foam-like MoS2-Au NPs nanostructure by a thermally decomposing method with nickel foam as substrates. The size and number density of the Au NPs can be further controlled by tuning the concetration of HAuCl4·3H2O. Benefit from their high specific surface area hierarchical porous structures, high dispersion and affinity of Au NPs in interconnected macroporous framework, the fabricated SERS substrates exhibit high sensitively. These SERS behaviors are also confirmed by theory calculation via a commercial COMSOL software. This new kind of 3D MoS2-Au NPs sample is expected to broaden the study in nano-electronic devices, especially in microanalysis. Acknowledgments The authors are grateful for financial support from the National Science Foundation of China (11474187, 11274204, 11674199 and 11504209), Excellent Young Scholars Research Fund of Shandong Normal University.
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References [1] M. Moskovits, J. Raman. Spectrosc. 36 (2005) 485-496. [2] K. Kneipp, H. Kneipp, J. Kneipp, Accounts. Chem. Res. 39 (2006) 443-450. [3] Alvarez-Puebla, A. Ramón, L.M. Liz-Marzán, Small. 6 (2010) 604-610. [4] M.P. Cecchini, V.A. Turek, J. Paget, A.A. Kornyshev, J.B. Edel, Nat. Mater. 12 (2013) 165-171. [5] A. Campion, P. Kambhampati, Chem. Soc. Rev. 27 (1998) 241-250. [6] D. Cialla, A. März, R. Böhme, F. Theil, K. Weber, M. Schmitt, J. Popp, Anal. Bioanal. Chem. 403 (2012) 27–54. [7] J.P. Singh, H.Y. Chu, J. Abell, R.A. Tripp, Y. Zhao, Nanoscale. 4 (2012) 3410–3414. [8] E.C. Le Ru, E. Blackie, M. Meyer, P.G. Etchegoin, J. Phys. Chem. C. 111 (2007) 1379413803. [9] S. Huang, X. Ling, L. Liang, Y. Song, W. Fang, J. Zhang, M.S. Dresselhaus, Nano. Lett. 15 (2015) 2892-2901. [10] M. Moskovits, PHYS. CHEM. CHEM. PHYS. 15 (2013) 5301-5311. [11] H. Qiu, Z. Li, S. Gao, P. Chen, C. Zhang, S. Jiang, H. Li, RSC. ADV. 5 (2015) 8389983905. [12] Z. Dai, X. Xiao, W. Wu, Y. Zhang, L. Liao, S. Guo, C. Jiang, LIGHT-SCI. APPL. 4 (2015) e342. [13] S. Su, C. Zhang, L. Yuwen, J. Chao, X. Zuo, X. Liu, L. Wang, Acs. Appl. Mater. Inter. 6 (2014) 18735-18741.
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[14] H. Zhou, F. Yu, C.F. Guo, Z. Wang, Y. Lan, G. Wang, Z. Ren, Nanoscale. 7 (2015) 9153-9157. [15] J. Lu, J.H. Lu, H. Liu, B. Liu, L. Gong, E.S. Tok, C.H. Sow, Small. 11 (2015)1792-1800. [16] Y. Shi, J.K. Huang, L. Jin, Y.T. Hsu, S.F. Yu, L.J. Li, H.Y. Yang, Sci. Rep. 3 (2013) 1839. [17] Q. Ding, Y. Shi, M. Chen, H. Li, X. Yang, Y. Qu, M. Sun, Sci. Rep. 6 (2016). [18] X. Yang, H. Yu, X. Guo, Q. Ding, T. Pullerits, R. Wang, M. Sun, Materials Today Energy. 5 (2017) 72-78. [19] Y. Qian, G. Meng, Q. Huang, C. Zhu, Z. Huang, K. Sun, B. Chen, Nanoscale. 6 (2014) 4781-4788. [20] C. Zhang, B.Y. Man, S.Z. Jiang, C. Yang, M. Liu, C.S. Chen, Z. Li, Appl. Surf. Sci. 347 (2015) 668-672. [21] T.S. Sreeprasad, P. Nguyen, N. Kim, V. Berry, Nano.Lett. 13 (2013) 4434-4441. [22] C. Lee, H. Yan, L.E. Brus, T.F. Heinz, J. Hone, S. Ryu, Acs. Nano. 4 (2010) 2695-2700. [23] J. Chen, T. Mårtensson, K.A. Dick, K. Deppert, H. Xu, L. Samuelson, H. Xu, Nanotechnology. 19 (2008) 275712. [24] A.Y. Polyakov, L. Yadgarov, R. Popovitz-Biro, V.A. Lebedev, I. Pinkas, R. Rosentsveig, R. Tenne, J. Phys. Chem. C. 118 (2014) 2161-2169. [25] F. Ochanda, W.E. Jones, Langmuir. 21 (2005) 10791-10796. [26] M. Moskovits, J. Chem. Phys. 77 (1982) 4408-4416. [27] M. Moskovits, J. Phys. Chem. 92 (1988) 6327-6329. [28] G. Lu, H. Li, C. Liusman, Z. Yin, S. Wu, H. Zhang, Chem. Sci. 2 (2011) 1817-1821. 15
[29] X. Ling, L. Xie, Y. Fang, H. Xu, H. Zhang, J. Kong, Z. Liu, Nano. Lett. 10 (2009) 553561. [30] A.M. Michaels, M. Nirmal, L.E. Brus, J. Am. Chem. Soc. 121 (1999) 9932-9939. [31] S. Nie, S.R. Emory, Science. 275 (1997) 1102-1106. [32] C. Zhang, S.Z. Jiang, C. Yang, C.H. Li, Y.Y. Huo, X.Y. Liu, B.Y. Man, Sci. Rep. 6 (2016). [33] E.C. Le Ru, E. Blackie, M. Meyer, P.G. Etchegoin, J. Phys. Chem. C. 111 (2007) 1379413803. [34] Z. Huang, G. Meng, Q. Huang, B. Chen, C. Zhu, Z. Zhang, J. Raman. Spectrosc. 44 (2013) 240-246. [35] C.C Kuo, C.H. Chen, Nanoscale. 6 (2014) 12805-12813.
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Highlights 1. We present a novel SERS substrate based on the MoS 2-Au NPs hybrids with a 3D framework. 2. 3D MoS2-Au NPs possess large specific area and the nanoporous structure increase the amount of the hot spots. 3. The size of gold nanoparticles is controlled by varying the concentration of HAuCl4·3H2O. 4. The morphologies and performance of 3D MoS 2-Au NPs were characterized by SEM, Raman spectroscopy, TEM, SAED, EDX and XRD. 5. We modeled the enhancement of the electric field of 3D MoS 2-Au NPs hybrids using FDTD analysis.
Graphical abstract
The three-dimensional MoS2 decorated with Au nanoparticles hybrids for surface-enhanced Raman scattering (SERS) sensing was demonstrated in this paper. The size of nanoparticles can be controlled by varying the concentration of HAuCl4·3H2O. Used R6G as the probe molecule, the prepared 3D MoS2-Au NPs hybrids has shown significant SERS ability. We modeled the enhancement of the electric field of MoS2-Au NPs hybrids using Finite-difference time-domain (FDTD) analysis, which can further give assistance to the mechanism understanding of the SERS activity.
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